Air-supported housing containing tesi printing drum



' April 8,1969 J. E. YOUNG 5 3,438,052 r AIR-SUPPORTED HOUSING C( JNTAI NING TEST PRINTING DRUM Fild Nov. 17. 1965 Sheet of s ATTORNEYS J. E. YOUNG April 8, 1969,

AIR-SUPPORTED HOUSING CONTAINING TESL PRINTING DRUM Sheet Filed Nov. 1'7. 1965 AIR-P Filed Npv. 17, 1965 April 1969 J. E. YOUNG 3,438,052

AIH-SUPPORTED HOUSING CONTAINING TESL PRINTING DRUM Sheet 3 Ora v INVENTOR;

JAMES, E. YOUNG FIG. 5

A TTOR/VEYS United States Patent 3,438,052 AIR-SUPPORTED HOUSING CONTAINING TESI PRINTING DRUM James E. Young, Pittsford, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Nov. 17, 1965, Ser. No. 508,272 Int. Cl. G01d /06 US. Cl. 346-74 6 Claims ABSTRACT OF THE DISCLOSURE An electrostatic printing apparatus in which the critical spacing between the recording web and the rotary printing drum is decreased by floating the drum within its housing on a thin pressurized film of air. An ion generating apparatus is also provided to replenish ions in the printing gap and to improve the reliability of the image on the recording web.

This invention relates to electrostatic recording and the reproduction of images.

It is known to record computer output information with high speed printers. A common way to do this is TESI printing (transfer electrostatic image), described in Us. Patents 2,919,967, 3,023,731, and 3,068,481, wherein electrostatic images are transferred in response to signal inputs to a recording medium at extremely high rates. The images are subsequently rendered visible by development techniques employing an electroscopic powder which adheres to the charged image areas in a manner well known in the xerographic art. In forming the latent image, it is usual to feed a recording web of insulating material between a rotary character drum and an array of backing electrodes. On receipt of an appropriate signal an electrostatic pulse is generated between a character on the drum and a corresponding backing electrode sufiicient to deposit an electrostatic charge pattern on the recording web.

Generally speaking, it is desirable to have the drum rotate at very high rates so that the information may be recorded as quickly as presented. It has been found that in a dynamic system such as that described above it is not possible to tolerate a spacing between the drum and web closer than about .003 of an inch without the rotating character drum marring the surface of the recording web. This has given rise to difficulties, since the wider the spacing between the recording web and drum, the greater the threshold voltage required for electrostatic transfer and the poorer theimage quality of the image produced. From the standpoint of image quality, of course, actual character contact with the recording web gives the best results, but for the reason stated above, such a system is not feasible with a rotating drum. Accordingly, the spacing to be maintatined is critical and has not been accomplished to complete satisfaction by prior art techniques.

Now in accordance with the present invention, it has been found that the critical spacing required for TESI printing can be more accurately and reliably maintained to effect a very high printout rate without detracting from image quality or incurring damage to the apparatus. With the instant invention a thin, pressurized film of air is provided for floating the rotary printing drum over the recording web. By regulating the air film pressure the printing gap can be controlled to effect optimum printing conditions.

It is therefore an object of this invention to provide an improved electrostatic recording apparatus.

It is a further object of this invention to provide an electrostatic printing apparatus wherein the printing gap is adjustable to close tolerances and uniformly maintained.

Another object of this invention is to provide an improved electrostatic printing apparatus having greater reliability of printout than heretofore.

For a better understanding of the invention, as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawings, wherein:

FIGURE 1 is an isometric illustration of the electro static printer with parts broken away to show details thereof;

FIGURE 2 is a partial bottom plan view of the rotary character drum housing shown in FIGURE 1;

FIGURE 3 is a sectional view taken along line 3-3 of FIGURE 2;

FIGURE 4 is a partial plan view for another embodiment of the invention in which the air film encircles the drum housing; and

FIGURE 5 is a sectional view along line 55 of FIG- URE 4.

Referring now to FIGURES 1-3, there is shown an electrostatic printer in accordance with the invention. The electrostatic images are formed on a dielectric sheet 10, such as Mylar web or any other dielectric substance having a suflicient resistance to hold an electrostatic image for a time period at least sufficient to permit development. Dielectric web 10 is arranged to pass tangentially under a rotating drum 11 which is rotatably mounted in generally U-shaped housing 13. Circumferentially disposed at equispaced points about drum 11 are several groups of alphanumeric character electrodes 19, each group consisting of a ring. The characters in each ring thereof are composed, for example, of the symbols A to Z and 0 to 9 so that both alphabetical and numerical information can be selectively recorded.

Supported below the web of reconding material 10 by a platen 20 is an array of stationary electrodes 21 disposed axially parallel to the drum 11, with one electrode for each ring of characters on the drum. Electrodes 21 are normally biased slightly below a threshold potential ranging from 200 to 500 volts by a voltage source 23. By means of a pulsing supply represented by block 24, electrodes 21 are activated to a potential above threshold to permit electrostatic recording at a corresponding position on the web. When a character on the ring representative of the input information is an-gularly aligned opposite the activated electrode, a field discharge is produced to form a charge pattern on the web having the shape of the selected character. The manner by which the characters are selected and the electrodes are activated is well known in the art as indicated, for example, in U.S. Patents 2,919,- 967 and 3,068,481, and it is intended that any suitable circuitry be used for this purpose.

When the insulating web is withdrawn from the electrostatic apparatus, it passes through a development mechanism, which is not shown, wherein the invisible electrostatic images are rendered visible by depositing thereon a finely divided material, such as an ink mist or an electroscopic pigmented resin powder which adheres to the charged image areas. A suitable powder development mechanism is fully disclosed, for example, in the Carlson Patent No. 2,357,809 and the Walkup and Fauser Patent No. 2,573,881, and a mechanism for developing electrostatic images with an ink mist is disclosed in Carlson Patent No. 2,551,582. The image can be rendered permanent as by fusing the image material to the web as is known in the art.

In accordance with the present invention, the housing 13 and consequently the rotating drum', are supported above dielectric sheet 10 on a cushion of air, as will be-v come more apparent, and by which the printing gap between drum 11 and sheet 10 may be accurately and uniformly maintained. Housing 13, which is desirably constructed from a lightweight material, such as fiberglass, has a pair of manifolds mounted on longitudinally extending opposite flanges 27. Each of manifolds 25 is connected to a source of compressed air 29 by means of conduit 31 that is provided with a control valve 33. As best shown in FIGURES 2 and 3, the bottom surfaces of flanges 27 include a plurality of individually Spaced recesses 35 communicating with each of manifolds 25 through restricted orifices 36. As can readily be appreciated, air supplied to manifolds 2 5 flows outwardly from recesses 35, as shown by the arrows, at a velocity and pressure differential sufficient to support housing 13 above the surface of web 10 on a thin air cushion.

Drum 11 is rotatably supported on a shaft 41 journaled in spaced walls of housing 13 in such a manner that the bottom periphery of drum 11 is tangent to a plane coextensive with the bottom of the housing. By varying the throttle position of valve 33, the air gap formed between the drum and dielectric web 10 can be regulated to permit spacings as close as .0005 inch. Extending from housing 13 are pins 43 that are received in elongated slots 45 of supporting brackets 47. In this manner, the housing can be displaced vertically but is precluded from skewing with respect to the path of the insulating web. Of course, if desirable, the housing and brackets may be set at a predetermined skewing angle Wtih respect to web 10. The number of supporting brackets 47 will depend upon the size and shape of the housing 13 and the two shown are intended to be illustrative only. One or more sutiable materials may be used for character drum 11 with the understanding that the electrode characters be electrically conductive. Preferably a lightweight drum, which may be rotated at speeds up to 40,000 r.p.m., comprises a plastic cylinder on which the electrode characters are formed by printed circuit techniques as are Well known by those skilled in the art.

To rotate the drum as best shown in FIGURE 1, there is provided an air driven turbine 51 mounted on drum shaft 41 exterior to housing 13. Turbine 51 consists of a series of blades 53 on which are directed a jet of compressed air from any suitable drive source, such as air supply 29, through a conduit 57 and valve 59 by Which it is possible to regulate the rotational speed of drum 11. Also provided on turbine 51 is an opening 60 for exhausting the air.

To rapidly dissipate ions with very high pulsing rates in an air gap that may be no more than two or three mils, depending upon the controlled setting of valve 33, a problem may arise as to the sutficient availability of ions for breakdown in the printing gap. To correct for this condition, a corona ion generator 61 is positioned inside the housing 13 to spray ions on the surface of drum 11 as it rotates in the direction of the printing gap, as best shown in FIGURES 3. Ion generator 61 consists of one or more corona wires arranged in parallel relation with the longitudinal axis of drum 11 and secured to the inside of housing 13. Due to the high angular velocity at which drum 11 is driven by air turbine 51, the drum periphery exerts a circulatory pressure fiow in the direction rotated causing the ions to flow toward the printing gap. As drum 11 rotates past ion generator 61, ions sprayed onto the surface of the drum are carried to the vicinity of the printing gap between the drum and dielectric web 10 replenishing the supply of ions that have been dissipated.

In order to further improve the reliability of the image on recording web 10, an electro-negative gas may be introduced to the printing gap as shown in the embodiment of FIGURES 4 and 5. The gas is contained within the drum chamber of housing 13 at a pressure less than that of the pressurized air cushion and is conveniently introduced through an aperture 65 in the top wall of housing 13 by means of a conduit 67 from a suitable source of supply. As best shown in FIGURE 4, recesses 35 in the bottom of housing 13 completely encircle the housing as does manifold 25 so that a curtain of pressurized air prevents the lower pressure gas from escaping through the bottom of the housing. It is believed the presence of the gas has the effect of sharpening the print by reducing the spread of the latent image fields due to its electro-negative properties. Any suitable gas may be used for effect ing improved fidelity of the latent image, such as Freon or one of the halogens.

Described above is a high speed electrostatic printer able to receive data at high information rates from a computer or the like and record it efficiently in a minimum of time. With the implementation of an adjustable air cushion between the rotary character drum and the recording web, the printing gap may be regulated to obtain maximum electrostatic transfer at a given threshold poteniial. At the same time, the character drum may be rotated at very high rates without incurring damage to either the surface of the recording web or drum. Heretofore, the dynamic parameters imposed upon the printer necessitated gap spacings that required much higher threshold potentials. Now in accordance with the present invention, gap spacings may be minimized and uniformly maintained to effect higher quality reproduction at reduced potentials. It is also to be realized that the reliability of the image is significantly improved by the introduction of both ions and an electronegative gas into the printing zone.

While there have been shown what are at present considered to be preferred embodiments of the invention, it will be obvious that many changes and modifications may be made without departing from the essential aspects of the invention. It is intended, therefore, in the appended claims to include any variations as fall within the true spirit of the invention.

What is claimed is:

1. Electrostatic printing apparatus comprising:

(a) contiguous walls forming a peripheral housing with an open bottom defined by a planar termination of said wall and having passages in the periphery of said contiguous walls extending to the bottom exterior of said housing,

(b) a drum rotatably supported within said housing and positioned to have the periphery thereof pass substantially tangent to a plane coextensive with the bottom of said housing;

(c) first electrode means representative of character information to be recorded positioned at the periphery of said drum;

(d) means for supporting an elongated length of a recording web in a path extending past the bottom of said housing in superposed relation with said passages and including second electrode means opposite to the rotational path of the first electrode means;

(e) means to selectively apply an energizing potential between said first electrode means and said second electrode means sufiicient to effect a field discharge from said first electrode means onto the web; and

(f) means for supplying compressed air from a source to said housing passages of pressure sufficient to float said housing and said drum to a predetermined spacing relative to said recording web on its support while said energizing potential is applied between said first and second electrode means.

2. Apparatus according to claim 1 wherein said means for supplying air includes a valve capable of being preset to control the spacing between said housing and said recording web.

3. Apparatus according to claim 1 including inlet means for introducing an electronegative gas into said housing in the vicinity of said drum.

4. Apparatus according to claim 1 including ion generating means within said housing for introducing ions into the printing gap between said electrode means whereby dissipated ions are replenished in said printing gap.

5. A high speed electrostatic TESI printing apparatus for recording information intelligence signals comprising:

(a) contiguous walls forming a peripheral housing with an open bottom defined by a planar termination of said walls and having passages in the periphery of said contiguous walls extending to the bottom exterior of said housing;

(b) a recording character drum rotatably supported in said housing and positioned to have the periphery thereof tangent to a plane coextensive with the bottom of said housing, said drum having a bank of electrode character rings thereon in a circumferential arrangement, each ring including a plurality of separate character shaped elements from which a signal can be recorded;

(c) means for rotating-said drum relative to said hous- (d) means for supporting a movable web of insulating material in a path tangentially parallel relative to said drum and including a linear row of backing electrodes arranged at positions corresponding to those of the rings;

e means to apply an energizing potential pulse between selective of said electrode characters and said backing electrodes sutficient to effect a field discharge from said pulsed electrode characters onto said web; and

(f) means for supplying compressed air to said passages in said housing including a settable valve whereby an air cushion of predetermined dimension may be formed between the bottom of said housing and said movable web during the electrical recording of signals on said web.

6. Electrostatic printing apparatus comprising:

(a) contiguous walls forming a peripheral housing with an open bottom defined by a planar termination of said walls and having passages in the periphery of said contiguous walls extending to the bottom exterior of said housing;

(b) a drum rotatably supported within said housing and positioned to have the periphery thereof pass substantially tangent to a plane coextensive with the bottom of said housing;

(0) air turbine drive means operatively connected to said drum for rotating said drum relative to said housing;

(d) first electrode means representative of character information to be recorded positioned at the periphery of said drum;

(e) means for supporting an elongated length of a recording web in a path extending past the bottom of said housing in superposed relation with said passages and including second electrode means opposite to the rotational path of the first electrode means;

(f) means to selectively apply an energizing potential between said first electrode means and said second electrode means sufiicient to effect a field discharge from said first electrode means onto the web; and

(g) means for supplying compressed air from a source to said housing passages of pressure sufiicient to float said housing and said drum to a predetermined spacing relative to said recording web on its support while said energizing potential is applied between said first and second electrode means.

References Cited UNITED STATES PATENTS 2,612,566 9/1952 Anderson 179-l00.2 3,023,070 2/1962 Benn 346-74' 3,195,142 7/1965 Benn 34674 3,208,076 9/1965 Mott 34674 3,229,268 1/1966 Solyst 179100.2

BERNARD KONICK, Primary Examiner.

F LEE J. SCHROEDER, Assistant Examiner.

US. Cl. X.R. 

